In a control device as disclosed in DE 41 29 509 C2, the hydraulic accumulator may be connected to the pressure medium source by a feed line. A stop valve operates between the operating cylinder and the accumulator, and is mounted directly in the feed line itself. The valve element of the stop valve has accumulator pressure applied to it in the direction of closing, and is relieved of pressure in the direction of opening.
In the disclosed system, the respective hydraulic accumulator is charged during raising of the load by the respective operating cylinder.
If the accumulator pressure rises to a value corresponding to the load pressure, a special seat valve intended for the purpose closes. The control compartment space of this seat valve is being charged with pressure. For connecting the respective hydraulic suspension accumulator to the respective operating cylinder, a three-way valve is automatically reversed. This process can take place automatically. The accumulator pressure then equals the load pressure on the piston side of the respective operating cylinder, since the hydraulic damping accumulator has been charged to this pressure by way of the feed line. The damping accordingly takes place at the pressure predominating in the piston space of the respective operating cylinder, not at a higher or lower pressure, which would additionally result in undesirable movement of the piston of the operating cylinder. Sagging of the load on connection of the respective hydraulic damping accumulator in particular is prevented. If, however, dynamic loads are applied to the hydraulic operating cylinder, ones in the form of peak loads, for example, which may occur when the operating machine in the form of a wheeled loader runs into material to be loaded, such as broken stones, soil, or the like, these peak loads damaging the damping accumulator are transmitted directly to the latter.
To prevent this occurrence, DE 39 09 205 C1 discloses, a conventional hydraulic system for construction machines such as wheeled loaders, tractors, or the like, a connecting line, branched off inside a main line leading to the hydraulic operating cylinders and provided with a stop valve. The stop valve is then bridged by the feed line, which in turn has a pressure reduction valve. The disclosed configuration allows charging the respective hydraulic accumulator during raising of the load by the respective hydraulic cylinder, specifically with a higher pressure determined by the pressure reduction valve. However, when the damping accumulator is connected by the stop valve to the piston side of the respective operating cylinder, the pressure on the piston side does not necessarily correspond to the higher damping pressure on the accumulator side, so that extension movement may unintentionally be transmitted to the operating cylinders and accordingly to the loading shovel.
U.S. Pat. No. 5,733,095 discloses a generic machine with a control device having at least one operating implement actuatable by at least one hydraulic operating cylinder, having a control block for control of the pressure medium paths between the operating cylinder, a pressure medium supply, and a tank, having at least one hydraulic accumulator, and having a stop valve mounted between the operating cylinder and the accumulator. The stop valve has a controllable valve element which is switched to its transmission direction for damping the movement of the operating cylinder. A switching valve that may be controlled by the control block is connected to the feed line of the hydraulic accumulator. The switching valve, when not actuated, blocks the feed line and the stop valve being connected to a secondary branch line connected to the feed line. Accumulator pressure is applied to such stop valve in the direction of opening, and is removed from such valve in the direction of closing. The disclosed solution allows charging the accumulator, independently of actuation of the operating cylinder, by means of the mechanism of pressure equalization between accumulator pressure and piston pressure. The disclosed hydraulic circuit is, however, of complicated design and requires a large number of components, so that such system is cost-intensive.